A known approach, ensuring that the traffic scheduling process stays in sync with the bandwidth usage by multicast services in the access network is based on IGMP correlation at the Broadband Network Gateway (BNG) or—more generally—at the traffic scheduling network node. IGMP correlation can be achieved by intercepting at the BNG upstream IGMP messages sent over a PPPoE (Point-to-Point Protocol over Ethernet) session to the BNG, or by using IGMP transparent snooping in the multicast replicating nodes. IGMP correlation at the BNG and IGMP transparent snooping are for instance described in section 6.3.2.3 and section 1.6 of DSL Forum Technical Report TR-101 entitled “Migration to Ethernet-Based DSL Aggregation”, published in April 2006 by the DSL Forum Architecture and Transport Working Group. Therein, the multicast replication nodes, e.g. the access nodes and aggregation switches, transparently snoop the IGMP join/leave messages which further travel upstream to the Broadband Network Gateway (BNG) in order to be intercepted there as IPoE (Internet Protocol over Ethernet) packets.
A drawback of IGMP correlation at the BNG, is that this solution results in high IGMP traffic towards the BNG, and consequently in high processing requirements for the BNG that has to deal with the high IGMP load.
Another drawback of IGMP correlation at the BNG, in particular the variant based on transparent snooping in the multicast replicating nodes, is that the BNG needs to determine to which access loops the IGMP messages refer in order to be able to update the traffic scheduling process. This requires the BNG to perform a correlation process between the source MAC and/or IP addresses of the IGMP message and the access loop identifier that is sent to the BNG at the time of PPP (Point-to-Point Protocol) or IP (Internet Protocol) session establishment. This complicates the overall decision process in the BNG.
An alternative model enabling concurrent, QoS aware deployment of unicast and multicast services, described in section 2.9, paragraph 2, of DSL Forum Technical Report TR-101 is based on distributed precedence and scheduling. In this model, the different services are marked according to a precedence relationship. Under congestion, traffic belonging to lower precedence classes will be dropped first. Although this model provides fairness between classes of a same precedence, it cannot establish fairness amongst users within the same class.
A further remark in relation to the prior art solutions, i.e. either the solution based on IGMP correlation or the solution based on distributed precedence and scheduling, is that these techniques may be implemented in a multi-BNG scenario, where the bandwidth is partitioned amongst two or more Broadband Network Gateways which each control the traffic within their partition. Although the static partitioning introduces limitations to the dynamic share of resources between multicast and unicast services, the multi-BNG implementations in general suffer from disadvantages similar to their single-BNG equivalent: multi-BNG solutions based on IGMP correlation put high IGMP processing requirements on the BNGs and require a more complex correlation process to be in place; multi-BNG solutions based on distributed precedence and scheduling on the other hand fail to establish fairness amongst users of a same class of service. An additional complexity introduced by multi-BNG solutions based on IGMP correlation is that measures must be taken in the network to ensure that IGMP messages arrive at all BNGs.
It is an object of the present invention to provide a multicast replicating network node and traffic scheduling network node that overcome the disadvantages of the above described prior art solutions. In particular, it is an object to define a multicast replicating network node and a traffic scheduling network node which enable traffic scheduling taking into account the bandwidth amounts occupied by multicast services in the access network, but with reduced processing requirements on the traffic scheduling network node.